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provide up to twice the erosion protection ofunreinforced vegetation. Vegetation is nature's best filter for removing sediment and other pollutants to safeguard water quality. When used with properly selected vegetation, TRivls are a cost-effective alternative to hard armor techniques such as rock rip-rap, concrete block systems, and concrete lined channels. e The flexible, three-dimensional matrix of a TRM improves the natural ability of plants to control erosion in several ways. The anchored synthetic mat reinforces the vegetative root structure to provide an erosion-resistant soft armor system. The mats also stimulate seed germination by providing an ideal mulch to hold moisture and warmth required for seed growth. Seedling development is accelerated because the mats provide conditions necessary to protect and nurture young plants. TRMs synergistically mesh with developing plant roots arld shoots. This is the most important function, because the mat provides lateral continuity between plants that reduces the risk oflocalized erosion of individual plants, shallow slippage, or rolling up of the soiJJroot matrix. By the time vegetation is fully established, the synthetic composite system becomes permanently anchored to the soil surface. The mats also increase ground cover and minimize development of weak spots from drought, fire, concentrated foot traffic. and other causes. e TRMs belong to a family of products known as "rolled erosion control products" (RECPs). A rolled erosion control product is defined as "a temporary degradable or long term non-degradable material manufactured or fabricated into rolls designed to reduce soil erosion and assist in the growth, establishment and protection ofvegetation.,,2 A "temporary degradable" RECP is "composed of biologically, photochemically, or otherwise degradable materials that temporarily reduce soil erosion and enhance the establislunent of vegetation" while a "long-term non- degradable" RECP is "composed solely of non -degradable materials that furnish erosion protection and extend the erosion control limits of vegetation for the de:sign life of a project.3 For instance, an "erosion control blanket" is a "temporary degradable RECP composed of processed natural or polymer fibers mechanically, structurally or chemically bound together to form a continuous matrix." A "turf reinforcement mat", on the other hand, is Ii "long-term, non- degradable REep composed ofUV stabilized, non-degradable syntheti<c fibers, nettings and/or filaments processed into three dimensional reinforcement matrices designed for permanent and critical hydraulic applications where design discharges exert velocities lwd shear stresses that a. exceed the limits of mature, natural vegetation.". The thickness, strength and void space of ., .. 3-